De kogel is door de kerk: as we already talked about earlier, Opera is going to switch to the WebKit engine, leaving its own Presto rendering engine behind. We didn't yet know if they would the switch only on mobile or on the desktop as well, and they cleared that up too: both mobile and desktop Opera Browsers will switch to the WebKit rendering engine.

developers get hired to create applications for what consumers have right now

Wrong. Every developer is hired to produce patches in the future. Nobody expects and can produce patches backwards. Nobody can actually change the past, not in software development, not in anything.

What you mean is that the patches that are produced land in a future product or future update of the product. If the product gets such updates is not a decision done by the developer, the project or the code-license.

In your case iPhones get updates including newer WebKit's at least a certain time till the whole product is EOL. Thats 100% an Apple decision.